This invention relates to a new and novel CRT device for generating a bright green light spot of the type particularly useful for projection color television.
Green light radiation for use in projection color television is generally produced by the electronic bombardment of a green luminescing terbium activated phosphor such as a terbium activated yttrium oxysulfide contained in a cathode ray tube.
A problem that has arisen from use of the terbium activated phosphor is that besides the desired fundamental radiation at 544 nm there are also significant radiations at 586, 490 and 620 nm. The radiation at 586 nm is the most troublesome as this radiation is the closest to the fundamental radiation and can cause blurring of the image when the 544 nm radiation is brought into focus.
In order to enhance the contrast of the projected image it has been suggested in Kikuchi et al IEEE Transactions on Consumer Electronics, Vol. CE-27, No. 3, August 1981, pp 478-484 to add a dye to an ethylene glycol-water coolant mixture sealed to the outside of the face plate of the CRT.
However, dyes generally have broad absorption bands and as a result not only is the reduction of the undesired emission achieved but there is also considerable reduction of the desired emission of the 544 nm band.
There is also disclosed in Ogloblinsky, U.S. Pat. No. 2,093,288 the addition of coloring agents to an oil bath located in contact with the outer surface of the face plate of a cathode ray tube in order to eliminate undesired components of light emitting from the phosphor screen of a projection television apparatus.
However, the use of coloring agents broadly, results in the same disadvantages as do the dyes employed by Kikuchi et al.